This application claims the priority of Korean Patent Application No. 2004-11483, filed on Feb. 20, 2004, in the Korean Intellectual Property office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a field emission device having a focusing control electrode and a field emission display, and more particularly, to a field emission device having a cathode electrode and a focusing control electrode disposed beneath a gate electrode and a field emission display (FED) including the same.
2. Description of the Related Art
Displays, essential for communicating information, have been adapted for use as personal computer and television monitors. Displays can be grouped into a cathode ray tube (CRT) which operates based on discharge of thermoelectrons at high speed, and a flat panel display which has widely been used in recent years. The flat panel display device includes a liquid crystal display (LCD), a plasma display device (PDP), and a field emission display (FED).
The FED is a display, in which a strong electric field is applied from a gate electrode to electron emission sources arranged on a cathode electrode with predetermined intervals therebetween, thereby emitting electrons from the electron emission sources, and emitting light by collision of the electrons onto a fluorescent material of an anode electrode. A micro tip that is made of a metal such as Mo has typically been used as the electron emission source of the field emission device in the conventional art. However, in recent years the metal tip has been replaced by a carbon nanotube (CNT). The field emission device employing a CNT provides advantages such as a wide viewing angle, high definition, lower power consumption, and temperature stability, and can thus be used in various applications such as car navigation and as a view finder of an electric image apparatus. Especially, the FED can be used as a substitute display for a personal computer, a personal data assistant (PDA) terminal, medical equipment, or high definition television (HDTV).
FIGS. 1 and 2 show two structures of a conventional field emission device.
Referring to FIG. 1, a conventional field emission device includes a substrate 10, a cathode electrode 11 stacked on the substrate 10, a first insulating layer 12, a first gate electrode 13, a second insulating layer 14, and a second gate electrode 15. The first and second insulating layers 12 and 14 have a cavity 17 having a predetermined diameter, and first gate hole 13a and a second gate hole 15a are formed on the first and second gate electrodes 13 and 15 so as to be aligned with the cavity 17. In addition, an electron emission source 19 is disposed on the cathode electrode 11, which is exposed through the cavity 17. A glass substrate is generally used as the substrate 10, and the cathode electrode 11 is formed of an indium tin oxide (ITO), that is, a conductive transparent material. The electron emission source 19 is generally made of CNT or the metal tip as described above.
Referring to FIG. 2, the conventional field emission device includes a substrate 20, a cathode electrode 21 stacked on the substrate 20, a first insulating layer 22, a first gate electrode 23, a second insulating layer 24, and a second gate electrode 25. In addition, a first cavity 27 and a first gate hole 23a, which have the same diameters, are formed on the first insulating layer 22 and the first gate electrode 23, and a second cavity 28 and a second gate hole 25a, which have larger diameters than that of the first cavity 27, are formed on the second insulating layer 24 and the second gate electrode 25. The CNT or the metal tip as the electron emission source is disposed inside the first cavity 27.
As shown in FIGS. 1 and 2, the field emission device having a dual-gate electrode structure controls a voltage applied to the second gate electrodes 15 and 25 to prevent an electron beam emitted from the electron emission sources 19 and 20 from diverging. Accordingly, the electron beam can be focused to a desired position with a beam spot of small size, such that higher image quality can be realized. Also, in a field emission display having the above described field emission device, an electric arc generated between the electron emission source and an anode electrode can be discharged through the second gate electrodes 15 and 25 that are arranged closer to the anode electrode. Therefore, the electric arc does not directly affect the electron emission sources 19 and 29 that emit the electron beam, the cathode electrodes 11 and 21, and the first gate electrodes 13 and 23.
Specifically, the field emission device having the structure shown in FIG. 1 having a narrow and deep cavity 17 and the gate holes 13a and 25a provides enhanced focusing of the electron beam emitted from the electron emission source 19. The field emission device having the structure shown in FIG. 2 has a wide second cavity 28 and a wide second gate hole 25a, and can thus be manufactured more easily.
FIG. 3 is a graph illustrating a simulation of electron speed at a position apart from the gate electrode. As shown in FIG. 3, electrons extracted by the gate electrode are accelerated while moving towards the anode electrode which faces the field emission device. Thus, the electron beam is more effectively focused at an initial stage of emission before the electrons are highly accelerated.
In a field emission device having the dual-gate electrode structures shown in FIGS. 1 and 2, the beam can be focused to a greater degree than that of a field emission device having a single gate electrode. However, when the electron beam is focused by a second gate electrode that is 5˜10 μm apart from the first gate electrode, it is the accelerated electron beam that is focused. Thus, the focusing efficiency is lowered.